PHYSICAL OCEANOGBAPHY OF THE GULF OF MAINE 
959 
The dynamic state is not so clear for the southwestern part of the banks area 
in summer, where the rise in temperature during the time interval between the two 
cruises of 1914 (July 20 to 21; August 25 to 26) may have been more than counter- 
balanced by some encroachment of water of high salinity inward over the shelf. 
Consequently, the dynamic values for the offing of Marthas Vineyard for that Au- 
gust are not directly comparable with those taken farther east during the month pre- 
ceding. However, no gradient is suggested sufficient to account for the repeated 
drifts of bottles westward around Nantucket Shoals from the vicinity of Cape Cod. 
The dynamic relationship along the continental slope in the offing of Marthas 
Vineyard and eastward about to longitude 68° for July and August, 1914 (fig. 203), 
recalls the March state (p. 939; fig. 188) so closely that a low or dynamic trough, 
with the gradient rising to seaward as well as shoreward, may be taken as typical of 
Fig. 204.— Dynamic gradient along the continental slope, bottom to 100 decibars, July to August, 1914. Contours for every 
dynamic centimeter 
this belt. Its circulatory implication has already been discussed (p. 939). At the 
date of our August profile for 1914 the calculated velocity of the easterly or “Gulf 
Steam” drift along the offshore edge of this low, and relative to the latter, was at 
least half a knot off Marthas Vineyard, or about the same as in March, 1920 (p. 939), 93 
which corresponds very well with the average velocities reported in this sector of the 
so-called “inner edge of the Gulf Stream” by passing ships in summer. 
The dynamic contours at 100 decibars for that July and August (fig. 204) show 
the easterly set actually washing the continental slope to the west of longitude 68° 
then swinging offshore. We have here a ready explanation for the fact that 
water of high temperature and high salinity — the “warm zone” — usually bathes the 
slope along this western section but is separated from the slope farther eastward by 
the colder counter drift out of the Eastern Channel. 
n For the reasons stated above (p. 939), the calculation of velocity in this region can be taken only as a rough approximation. 
